Other Boron Nitride Structures

Polycrystalline boron nitride films with a structure similar to ihombo-hedral boron carbide and a ratio of boron to nitrc en of 3 1 were produced by hot-filament CVD. This work indicates the possible existence of odier boron nitride structures.  

Hafnium nitride (HfN) is a refractory which is resistant to chemical attack. It is produced by CVD mostly on an experimental basis. Its properties and characteristics are summarized in Table 10.4. 

Lattice Parameter a = 0.452 nm Space Group Fm3m Pearson Symbol cF8 Composition HfNo 7510 HFNj 12 Molecular Weight 192.497 Color greenish yellow X-ray Density 13.8 g/cm Melting Point 3387°C Debye Temperature 421 K 

Heat of Formation (-AHf) at 298K 369.4 kJ/g-atom metal Thermal Conductivity (K) 21.7 W/m °C Thermal Expansion 6.9 x 10 V°C 

Superconductive Transition Temperature 2-8.7 K (varies with composition) 

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We have shown some of the structures exhibited by inorganic compounds. Others will be described as we examine the chemistry of particular elements and their compounds. Also, a great many covalent extended structures (e.g., diamond, graphite, quartz, boron nitride, etc.) will be discussed in later chapters as we deal with the chemistry of those materials. The discussion presented here is sufficient to serve as a basis for describing the behavior and properties of many inorganic substances. This is an important objective for understanding descriptive chemistry. 

Boron phosphide occurs in two forms, one of which, cubic BP, has a diamondlike structure analogous to cubic boron nitride (see above). The other variety, Bi2PL8, has a partially disordered crystal structure that contains icosahedral Bi2 units, as found in many metal borides (Section 5-3). Cubic BP is extremely inert, resisting attack by boiling concentrated acids or bases, is not oxidized in air below... 

In covalent azides, the pseudohalogen azide RN3 has an angular structure as in HN3. Triazidoborazine [H3N3B3(N3)3] and other boron azides, for example, salts of the tetraazidoborate ion B(N3 (4 have been considered as boron nitride precursors (see Boron-Nitrogen Compounds). The M(Ns)3 azido complexes of the other group 13 elements (Al, Ga, In, Tl) and their M(N3)4 tetraazido anions are all known. They and their derivatives are also used as precursors for the nitrides. 

There are three polytypes of boron nitride (BN), namely those with cubic(c-BN), wurtzite-type(w-BN) and hexagonal(h-BN) structures. Because the ELNES spectrum reflects the difference of the local structure, ELNES for h-BN, which has a graphite-type layered structure, shows considerably different spectrum from the other polytypes " " as shown in Fig.20. Among these polytypes, the near edge structures for c- and w-BN resemble each other, because of the similarity of their stmctures. As mentioned above. 

Figure 1 shows the two models which were calculated. The base structure was considered with another research group for improvement of the thermal conductivity, while three layered structure was adopted on the view point of shielding. The base structure was assumed to be a concentric cylinder of 60 cm height which was formed void, strontium titanate ( "SrTiOs, P 5.12g/cm 0 and boron nitride (BN, p 2.26g/cm3) from the inside. The weight of these two materials was made to be identical each other. 

Boron nitride BN can form two solid structures, one containing hexagonal BN layers similar to graphite, and the other with tetrahedral sp bonding like diamond (see Topic D21. Borazine B- n3h6... 

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